This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application 2000-289400 filed on Sep. 22, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a variable valve timing system of an internal combustion engine. More particularly, the present invention pertains to a variable valve timing system for controlling the opening and closing timing of an intake valve and an exhaust valve in an internal combustion engine.
A known variable valve timing system is disclosed in Japanese Patent Laid-Open Publication No. 09(1997) 324613 published on Dec. 16, 1997. The disclosed variable valve timing system includes a housing member rotating as a unit with either a crankshaft or a camshaft of the internal combustion engine, and a rotor member rotating as a unit with either the camshaft or crankshaft. The rotor member is rotatably assembled on a shoe portion provided at the housing member and forms an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member. The variable valve timing system also includes a relative rotation controlling mechanism which allows relative rotation of the housing member and the rotor member by an unlock operation the supply of an operation fluid. The relative rotation controlling mechanism also restricts relative rotation of the housing member and the rotor member by a lock operation through the discharge of the operation fluid at a lock phase within an intermediate area from a most advanced angle phase to a most retarded angle phase excluding rotation limited phases at both ends. The variable valve timing system further includes a fluid pressure circuit for controlling the operation fluid to be supplied to and discharged from the advanced angle chamber, the retarded angle chamber, and the relative rotation controlling mechanism.
In the above-mentioned variable valve timing system, the passage connecting the advanced angle chamber and the relative rotation controlling mechanism with the fluid pressure circuit, and the passage connecting the retarded angle chamber and the relative rotation controlling mechanism with the fluid pressure circuit always communicate under the same condition. The fluid pressure of the operation fluid supplied to the advanced angle chamber and the relative rotation controlling mechanism, or the fluid pressure of the operation fluid supplied to the retarded angle chamber and the relative rotation controlling mechanism are each approximately the same pressure all the time. Accordingly, when the relative rotation of the rotor member and the housing member is restricted at the lock phase by the relative rotation controlling mechanism, when the operation fluid is rapidly supplied (phase control for quick response) to the advanced angle chamber through the relative rotation controlling mechanism or to the retarded angle chamber through the relative rotation controlling mechanism both from the fluid pressure circuit, the relative rotation of the rotor member and the housing member is started before the unlock operation of the relative rotation controlling mechanism is completed. Thus a lock member of the relative rotation controlling mechanism can be caught in the relative rotation of the rotor member and the housing member.
Additionally, in the above-mentioned variable valve timing system, the rotor member is rotated by the fluctuation torque of the camshaft in the lock phase, and the pressure of the operation fluid filled in the advanced angle chamber or the retarded angle chamber is increased because the volume of the advanced angle chamber or the retarded angle chamber becomes smaller by the rotation of the vanes. The increased pressure of the operation fluid causes movement of the lock member (unlock operation) and unintended operation of the relative rotation controlling mechanism.
In light of the foregoing, a need exists for an improved variable valve timing system which is not as susceptible to the drawbacks discussed above.
According to one aspect of the invention, a variable valve timing system includes a housing member rotatable as a unit with either a crankshaft or a camshaft of an internal combustion engine, and a rotor member relatively rotatably assembled on a shoe portion of the housing member and forming an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member, with the rotor member rotating as a unit with either the crankshaft or the camshaft of the internal combustion engine. A relative rotation controlling mechanism allows relative rotation of the housing member and the rotor member by an unlock operation through supply of an operation fluid, and restricts relative rotation of the housing member and the rotor member by a lock operation through discharge of the operation fluid at a lock phase within an intermediate area from a most advanced angle phase to a most retarded angle phase excluding rotation limited phases at both ends. A fluid pressure circuit controls the operation fluid to be supplied to and discharged from the advanced angle chamber, the retarded angle chamber, and the relative rotation controlling mechanism. The relative rotation controlling mechanism includes a first controlling mechanism restricting the relative rotation to an advanced angle side when the first controlling mechanism is operated under the lock operation at the lock phase, and a second controlling mechanism restricting the relative rotation to a retarded angle side when the second controlling mechanism is operated under the lock operation at the lock phase. The fluid pressure circuit supplies and discharges the operation fluid to or from the advanced angle chamber through the first controlling mechanism, and supplies and discharges the operation fluid to or from the retarded angle chamber through the second controlling mechanism. A first passage connects the advanced angle chamber with the first controlling mechanism and functions as a throttle, and a second passage connects the retarded angle chamber with the second controlling mechanism and functions as a throttle.
When used in a variable valve timing system for an automobile, the throttle function of the advanced angle side and the retarded angle side is desirably canceled when the rotor member is rotated relative to the housing member to the advanced angle side or the retarded angle side from the lock phase by more than a predetermined amount.
At an early stage of starting of the internal combustion engine, the operation fluid is not sufficiently discharged from the fluid pressure circuit to each advanced angle chamber, each retarded angle chamber, the first controlling mechanism, and the second controlling mechanism. Thus, the relative rotation phase of the rotor member to the housing member cannot be adjusted or maintained. If the relative rotation phase of the rotor member to the housing member is not positioned at the intermediate lock phase, the housing member and the rotor member are relatively rotated by torque fluctuation affecting the camshaft. In this manner, when the relative rotation phase of the rotor member to the housing member is positioned at the intermediate lock phase, the relative rotation to the advanced angle side is restricted by the first controlling mechanism, and the relative rotation to the retarded angle side is restricted by the second controlling mechanism. Then the relative rotation of the housing member and the rotor member is restricted and maintained at the intermediate lock phase by the first controlling mechanism and the second controlling mechanism, and the starting performance of the internal combustion engine is improved.
As explained above, when relative rotation of the housing member and the rotor member is restricted by the first controlling mechanism and the second controlling mechanism at the intermediate lock phase, when the operator fluid is sufficiently supplied to each advanced angle chamber through the first controlling mechanism from the fluid pressure circuit, or to each retarded angle chamber through the second controlling mechanism from the fluid pressure circuit, the first passage connecting the advanced angle chamber which the first controlling mechanism functions as a throttle and the second passage connecting the retarded angle chamber with the second controlling mechanism also functions as a throttle.
Accordingly, in the passages to which the operation fluid is supplied, the fluid pressure provided to the first controlling mechanism or the second controlling mechanism is instantly obtained, and the unlock operation is immediately conducted. At the same time, the supply of operation fluid is controlled to the advanced angle chamber and the retarded angle chamber by the throttle function of both passages. Then the relative rotation of the housing member and the rotor member is relatively slower compared to the unlock operation. Thus, when the phase is controlled for quick response, the lock members of the first controlling mechanism and the second controlling mechanism cannot be caught in the relative rotation of the housing member and the rotor member.
When the rotor member is rotated to the advanced angle side or the retarded angle side from the lock phase relative to the housing member by more than the predetermined amount, the throttle function of the advanced angle side and the retarded angle side is configured to be canceled. Thus at the lock phase, the throttle function is effectively operated, and when the rotor member is rotated relative to the housing member to the advanced angle side or the retarded angle side from the lock phase by more than the predetermined amount, the operation fluid is thoroughly supplied to the advanced angle chamber from the first controlling mechanism or to the retarded angle chamber from the second controlling mechanism. Then the rotor member is relatively rotated to the housing member with a good response. Accordingly, a reliable or certain unlock operation and good response can be obtained.
According to another aspect of the invention, a variable valve timing system includes a housing member rotatable as a unit with either a crankshaft or a camshaft of an internal combustion engine, and a rotor member relatively rotatably assembled on a shoe portion of the housing member and forming an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member, with the rotor member rotating as a unit with either the crankshaft or the camshaft of the internal combustion engine. A relative rotation controlling mechanism allows relative rotation of the housing member and the rotor member by an unlock operation through supply of an operation fluid, and restricts relative rotation of the housing member and the rotor member by a lock operation through discharge of the operation fluid at a lock phase within an intermediate area from a most advanced angle phase to a most retarded angle phase excluding rotation limited phases at both ends. A fluid pressure circuit controls the operation fluid to be supplied to and discharged from the advanced angle chamber, the retarded angle chamber, and the relative rotation controlling mechanism. The relative rotation controlling mechanism includes a first controlling mechanism restricting the relative rotation to an advanced angle side when the first controlling mechanism is operated under the lock operation at the lock phase, and a second controlling mechanism restricting the relative rotation to a retarded angle side when the second controlling mechanism is operated under the lock operation at the lock phase. The fluid pressure circuit supplies and discharges the operation fluid to or from the advanced angle chamber through the first controlling mechanism, and supplies and discharges the operation fluid to or from the retarded angle chamber through the second controlling mechanism. A first passage having a first narrow portion communicates between the advanced angle chamber and the first controlling mechanism, and a second passage having a second narrow portion communicates between the retarded angle chamber and the second controlling mechanism.